Since my last review of Firefox, the independent Web browser has undergone its biggest appearance overhaul in more than three years. New rounded tabs and a button-filled settings panel instead of a traditional menu are the most noticeable changes. But more subtle differences have also snuck in, such as more-powerful syncing and tons of new support for emerging Web standards. Firefox has constantly been improved in speed and design, as well as with the addition of features like built-in PDF reading and outstanding support for new Web technologies. It may be time for another look if you're a lapsed Firefox user. I know I've been re-converted.

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Installation Firefox is available on the most platforms of any browser: Mac and Linux, as well as Windows 8, 7, Vista, and XP—even Internet Explorer 11 can't claim the last two. Like Google Chrome, however, it's not a native 64-bit application, and it can't function as a modern Windows 8.1 full-screen app. If you're already a Firefox user, all you have to do is restart the browser to get the new version. You can import bookmarks from any other installed browsers on first run, and the setup is easy as Chrome's. Firefox makes it easy to choose any search provider, and there's a Firefox with Bing version, which uses Microsoft's Web search built in.

A New LookFirefox's new design borrows from its Android sibling, and it's the best-looking browser interface around. The new look resembles that of Chrome, but there are real differences: Chrome's tabs aren't rounded, and they don't recede into the window border when they don't have the focus, as Firefox's do. Firefox also keeps the search box separate from the address box—an important privacy protection, as browsers that use a single box typically send everything you type there to a search provider.

Firefox's new-tab page has finally fully caught up to those of other browsers, with tiles for your most frequently visited sites and a search box for the search provider of your choice. I do, however, miss Internet Explorer's "Recently closed tabs" choice on this page, though the Firefox default start page does offer this option, along with big buttons for downloads, bookmarks, and settings. If you just want a blank new tab, the grid button at top right grants your wish.

Like many modern apps, Firefox now sports the three-dash "hamburger" menu button. When clicked, this drops down not a standard text menu, but rather a panel of icons for settings, add-ons, and more. It's very clean and less overwhelming than the multiple unfolding text menus found in previous versions (and still found in Chrome).

Keeping with the Firefox tradition of customizability, an always-present choice at the bottom of this panel is "Customize," which switches the browser to a mode that lets you change any of its buttons in either the panel itself or in the toolbar next to the search bar.

You can eliminate the browser's top title bar for the "tabs on top" look, or toggle standard text-based menu options and the bookmarks bar, too.

Firefox's new bookmarking tool is also a welcome convenience. Its double button consists of star and clipboard icons. When you tap the star, an adorable animation flies it over to the clipboard, and the star button turns blue, showing that the current site has been added to your bookmarks. Tapping the clipboard button opens a dropdown showing all or recent bookmarks.

You can also summon a full bookmark sidebar or separate window for a view of your bookmarks. The History button similarly offers a sidebar option (though its button isn't by default atop the browser), and each includes a search bar. Internet Explorer's combined favorites/history button seems a better approach for quicker access. In Chrome, you have to go through menus to get to either.

Better SyncingI've long been a fan of Firefox's syncing capabilities, which not only let you see your bookmarks and settings in any instance of the browser on any device, but also even let you continue a browsing session from machine to machine. You can sync passwords and form data as well. The new syncing method is much easier to set up. Before, you had to enter a generated code in any new device; now you simply sign in. The synced information is encrypted end to end, according to Mozilla.

When setting up, you can either have everything synced, or specify sync items. Chrome makes it harder to fine-tune what's synced. After responding to a confirmation email, you'll see the Welcome to Sync page, with a big Manage button to specify what you want synced. This just opens an old-fashioned sync settings dialog. One issue with Firefox syncing is that it only supports Android mobile platform, so those 800 million iOS devices are out of luck, not to mention the Windows Phone faithful.

Tab Groups (Panorama) and Pinned Tabs Firefox's unique Panorama feature offers a revolutionary way to organize tab groups and will be especially popular among those who like to have lots of tabs open. It's no longer on by default, but you can add its Mondrian-looking icon from the Customize Toolbar dialog; tapping the button shows rectangles with page thumbnails.

You can drag tabs among groups and resize and move the group boxes themselves around. You can even give a name to a tab group to keep it organized. When you click on a page thumbnail in any tab group, that page will maximize in the browser window, and you only see tabs from its group.

If there are sites you always want access to, you can pin their tabs to the left side of the tab bar—just as you can in Chrome. These pinned tabs appear narrower, showing just the site icon. The pinned sites also load automatically when you start Firefox. But you can't create an app shortcut icon for use on your desktop or Windows 7 taskbar, as you can with Internet Explorer and Chrome.

Standards and New Code SupportFirefox has long been at the forefront of Web technology innovation. The latest version not only supports the lion's share of HTML5 features, but also other emerging standards such as WebRTC, which gives the browser access to your webcam and microphone for things like live video chat. Another technology Mozilla has led is Emscripten and asm.js, which allow native-code performance for processing-intensive Web apps such as 3D gaming.

Firefox supports Web Audio API, along with more than 30 other Web APIs, many of which were prompted by Mozilla's Firefox OS mobile platform initiative. These let the browser do things such as answer phone calls, control device vibration, detect the screen orientation, and more. But several apply to desktop browsing, too, such as mouse-lock and geolocation APIs. The browser also supports the faster SPDY replacement for HTTP, the basic networking communications protocol of the Web.

Many of Firefox's capabilities are not included on Niels Leenheer's HTML5Test website (see performance table on the next page), which tests for its own set of chosen emerging standards and W3C HTML5 recommended ones. Another reason that test should be taken with a large grain of salt is that it doesn't actually test whether the functions are correctly implemented, just that the browser acknowledges the function calls.

On another often-cited standards testing site, Acid3, Firefox passes with 100 percent. We're still waiting for an official test for HTML5 from the W3C, the Web coding's governing body. For what it's worth, HTML5 is only expected to finally become a recommended standard this year.

Michael Muchmore is PC Magazine’s lead analyst for software and Web applications. A native New Yorker, he has at various times headed up PC Magazine’s coverage of Web development, enterprise software, and display technologies. Michael...

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